U-Pb isotopic evidence for the accretion of different crustal blocks to form the Lewisian Complex of northwest Scotland

Kinny, Peter D.; Friend, C. R. L.

doi:10.1007/s004100050340

Cited by 104 publications

(88 citation statements)

References 28 publications

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“…Northwest of the leading edge of the Moine Thrust, rocks of the Laurentian foreland crop out both on the Scottish mainland and in the Outer Hebrides. The Lewisian gneisses of this foreland have Archaean protoliths that have been affected by several, subsequent, high-grade metamorphic and deformation events (Lyon and Bowes, 1977;Kinny and Friend, 1997;Park and Tarney, 1987;Cliff and Rex, 1989;Friend and Kinny, 1995;Friend and Kinny, 2001;Kinny and Friend, 2005). The occurrence of 1.08 Ga eclogites at Glenelg implies that the Caledonian in the northwest experienced crustal thickening by imbrication (Sanders et al, 1984).…”

Section: Potential Magma Sources In the Crust And Mantlementioning

confidence: 98%

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

Clemens

Darbyshire

Flinders

2009

Lithos

111

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The 425 Ma Arrochar and Garabal Hill-Glen Fyne complexes of highland Scotland are examples of post-orogenic magmatism accompanying extensional collapse of an orogen, in this case the Caledonian. The rocks are dominantly high-K series, but range from medium-K to shoshonitic. Mantle upwelling, melting and the intrusion of large volumes of mafic magma into the crust are inferred to have accompanied lithospheric thinning, and to have provided the heat source for melting of young arc crust accreted during the preceding subduction epoch.Fluids evolved from the subducting slab are inferred to have caused high degrees of enrichment in the overlying mantle wedge. Deep in the crust, the mantle-derived, K-rich mafic to intermediate magmas mixed with felsic crustal melts to form the spectrum of magmas intruded in the two complexes. Microgranular enclaves in the granitic rocks represent mafic magmas derived from the enriched mantle and hybridised by reaction, diffusion and mechanical mixing with their host felsic magmas, but they do not form part of the evolutionary series that produced the host magmas. Rather than inheriting its LILEenriched character directly from crustal melts, or from crustal assimilation by mafic magmas, the high-K series may commonly owe at least part of its potassic character to the involvement of mantle (highly metasomatised by slab-derived fluids) as a major magma source. Enclave suites, though prominent in some granitic rocks should not be assumed to represent magmas that played a significant role in the production of the chemical variations in their host magmas.

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Section: Potential Magma Sources In the Crust And Mantlementioning

confidence: 98%

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

Clemens

Darbyshire

Flinders

2009

Lithos

111

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“…For the mainland Lewisian Gneiss Complex, the Rhiconich block is predominantly composed of migmatitic gneisses of amphibolite grade and of broadly granodioritic composition (Kinny and Friend, 1997;Goodenough et al, 2010). Protolith ages are in the range of 2840-2680 Ma with rare inherited ages of c. 3000 and 3550 Ma (Kinny and Friend, 1997;Friend and Kinny, 2001).…”

Section: Regional Geologymentioning

confidence: 99%

“…Protolith ages are in the range of 2840-2680 Ma with rare inherited ages of c. 3000 and 3550 Ma (Kinny and Friend, 1997;Friend and Kinny, 2001). The Rhiconich and Assynt blocks are separated by the Laxford Shear Zone (Evans, 1965;Corfu et al, 1994;Goodenough et al, 2010;.…”

Section: Regional Geologymentioning

confidence: 99%

High-precision U–Pb dating of complex zircon from the Lewisian Gneiss Complex of Scotland using an incremental CA-ID-TIMS approach

2015

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“…An important limitation to these techniques, however, is that ionization of complex matrices has led to the restriction of the methods largely to zircon dating; dates based on monazite-(Ce), (Ce,La,Th)PO 4 , and xenotime-(Y), YPO 4 , have recently been documented (e.g., , McNaughton et al 1999, Stern & Berman 2000. The dating of other phases has only rarely been attempted (e.g., titanite: Kinny & Friend 1997;allanite: Catlos et al 2000).…”

Section: Background Informationmentioning

confidence: 99%

LASER-ABLATION U Th Pb IN SITU DATING OF ZIRCON AND ALLANITE: AN EXAMPLE FROM THE OCTOBER HARBOUR GRANITE, CENTRAL COASTAL LABRADOR, CANADA

Cox¹,

Wilton²,

Košler³

2003

The Canadian Mineralogist

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U-Th-Pb geochronology based on data acquired by laser-ablation microprobe -inductively coupled plasma -mass spectrometry (LAM-ICP-MS) has been applied to in situ dating of allanite and zircon in a single section of the October Harbour granite, Labrador. This is the first report of Th-Pb dating of allanite by the LAM-ICP-MS method, confirmed by zircon ages from the same section. Crystals as small as 20 ϫ 20 m have been analyzed in a standard polished section 100 m thick. Zircon crystals were examined using back-scattered electron images to identify features such as inherited cores, overgrowths and oscillatory growth. In this study, 45 LAM-ICP-MS analyses were carried out on 35 crystals of zircon. The U-Th-Pb zircon data suggest that the age of the granite is 1657 ± 10 Ma (MSWD = 0.77, weighted mean 207 Pb/ 206 Pb ages from 25 concordant points). The data also indicate 1800-1850 Ma inheritance and patterns of multiple loss of lead in many grains. The allanite occurs as large euhedral crystals; they show elevated U and Th contents. Twenty-six analyses of two such crystals of allanite gave sixteen concordant points, obtained mainly from the low-Th core of a single large crystal, and a weighted mean Th age of 1635 ± 17 Ma (MSWD = 2.1). Although complex Pb-loss is also recorded in portions of the allanite crystals analyzed, no evidence of inheritance was recorded. The age of the October Harbour granite is constrained to be ca. 1640-1660 Ma; it thus is significantly younger than the previously defined conventional multi-grain U-Pb zircon age of 1719 ± 3 Ma attributed to the postulated parental intrusive complex, the Strawberry intrusive suite. The Strawberry suite thus may not be a single ca. 1720 Ma suite of rocks, but a more complex composite unit represented by rocks of widely differing ages. Mots-clés: ablation au laser, analyses ICP-MS, geochronologie U-Th-Pb, datation in situ, zircon, allanite, granite de October Harbour, Labrador.

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U-Pb isotopic evidence for the accretion of different crustal blocks to form the Lewisian Complex of northwest Scotland

Cited by 104 publications

References 28 publications

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

High-precision U–Pb dating of complex zircon from the Lewisian Gneiss Complex of Scotland using an incremental CA-ID-TIMS approach

LASER-ABLATION U Th Pb IN SITU DATING OF ZIRCON AND ALLANITE: AN EXAMPLE FROM THE OCTOBER HARBOUR GRANITE, CENTRAL COASTAL LABRADOR, CANADA

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